GB2244125A

GB2244125A - Heat storage units

Info

Publication number: GB2244125A
Application number: GB9010981A
Authority: GB
Inventors: Gordon Ellis
Original assignee: Creda Ltd
Current assignee: Creda Ltd
Priority date: 1990-05-16
Filing date: 1990-05-16
Publication date: 1991-11-20
Also published as: GB9010981D0; ES2025510A6; JPH04227476A

Abstract

A heat storage unit comprises a heat store consisting of a stack of bricks, which are electrically heated by means of elements so as to take advantage of off-peak electricity. A secondary hot water heating circuit is heated by means of a primary circuit which includes a heat exchanger in contact with the store, in which water is super heated. The heat exchanger comprises chambers (17, 18, 19) consisting of opposed plates which are closely spaced together, since a large area is available for contact with the bricks lying between the plates and the force urging the bricks apart due to thermal expansion of the chambers is relatively weak. Depressions (20) in each plate abut corresponding depressions in an opposing plate. <IMAGE>

Description

Heat Storaqe Unit This invention relates to heat storage units.

The invention is particularly concerned with heat storage units comprising a heat store, electrical means for heating the heat store, and a heat exchanger in contact with the heat store for heating a fluid to enable heat to be withdrawn from the heat store. For example, heat could be withdrawn from the store by introducing water into the heat exchanger in a primary circuit, and using heat communicated to a secondary circuit to heat hot water radiators and other heat dissipation means. The charging of the heat store will usual be effected during periods of a daily cycle when electricity is available at a reduced rate, a so-called off-peak period, which could be between midnight and 7 am.

Water can be introduced into the heat exchanger during the remainder of the 24 hour period when it is desired to withdraw heat from the heat store.

It has been proposed simply to use upright tubes connected at the top and bottom ends of the heat exchanger, the heat store consisting of pairs of bricks with semi-cylindrical recesses which together surround the tubes.

However, the inevitable expansion and contraction of the tubes during their heating and cooling cycles tends to force the pairs of bricks surrounding the tubes apart and thus impair their thermal contact with the tubes and, since the tubes are relatively strong, any departure from the original shape due to thermal stresses is also likely to impair the thermal contact.

The invention provides a heat storage unit comprising a heat store, electrical means for heating the heat store, and a heat exchanger in contact with the heat store for heating a fluid to enable heat to be withdrawn from the heat store, the heat exchanger including a chamber defined by opposed plates, the spacing of which is small relative to the lateral dimensions of the plates.

The use of a heat exchanger region defined by opposed plates permits a large area of contact with the heat store, and the portions of the heat store on each side are unlikely to be displaced greatly during thermal cycling because the thickness of the region and hence the material defining the region is relatively small.

The heat exchanger may include a number of such chambers, arranged upright, and the heat store may comprise bricks which can be slotted in between and on either side of the chambers.

A domestic hot water system including a heat storage unit constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of the hot water system; Figure 2 is a perspective view of the heat exchange assembly of the heat exchange unit; Figure 3 is a front elevation seen along the lines 3-3 of Figure 2; Figure 4 is a section taken along the lines 4-4 of Figure 3; and Figure 5 is a perspective view of a part of the heat store.

Referring to Figure 1, the hot water system includes a heat storage unit indicated generally by the reference numeral 1 having a primary water/steam circuit indicated generally by the reference numeral 2, which in turn heats a secondary hot water circuit indicated generally by the reference numeral 3.

A water pump 4 pumps the hot water in the secondary circuit around fan-assisted water pipe coils 5, 6. The secondary circuit could include hot water radiators or other heat dissipation means, positioned within the rooms to be warmed.

The primary water/steam circuit includes a heat exchanger indicated generally by the reference numeral 7 in thermal contact with heat storage bricks 8 surrounded by insulation panels 9 - 12. The bricks are heated by means of heating coils 13, and are intended to be energised by off-peak electricity, which is available at a reduced price during a 24 hour period, from a separately metered power source.

When the bricks have been heated to a high temperature, water is allowed to pass from a reservoir tank 14 by means of a control valve 15 by gravity into the lower end of the heat exchanger 7, where the water is evaporated into super-heated steam. The steam gives up its heat in an additional heat exchanger 16 (to the secondary circuit) and condenses back into water which is collected in reservoir tank 14. The control valve 15 enables the return condensed flow to be interrupted so that all the primary circuit water is retained in the reservoir 14 in order that the withdrawal of heat from the primary circuit can cease.

In accordance with the invention, the heat exchanger 7 consists of three identical chambers 17, 18, 19 (Figure 2), each fabricated from 2 opposed, dished, sheets of metal welded together along flanges defining the rims of the dishes. Each sheet has a number of depressions 20 formed in it, which abut corresponding depressions in the opposed sheet, in order to space the sheets of metal apart. Five depressions are shown but other numbers of depressions could be used. Each chamber is connected at its front upper corner and rear lower corner to respective upper and lower header pipes 21, 22, which communicate with the primary circuit.

The heat storage unit is delivered to the user with the heat exchanger in position, and bricks are inserted between the chambers, two or more deep. The bricks are laid in courses and the heating elements 13 connected in series are laid into the recesses 23 of the bricks of that course. Subsequent courses are laid in the same way.

The construction of the heat exchanger assists in servicing of the heat exchange unit, since the heat exchanger can be withdrawn from the outer casing, after the bricks have been withdrawn simply by removing the upper insulation panel 11. The pipes connecting the heat exchange chambers with the lower headers do not pass through the lower insulation panel 12.

Among other advantages of the design of the heat exchanger are: a large area of contact with the storage brick for the enhancement of heat transfer therefrom; the thermal deformation forces on the bricks are relatively weak; the thermal deformation that does take place increases the quality of thermal contact with the brick; and the volume of water needed to fill the heat exchanger is minimised, thereby making for quieter operation because this water must be driven out of the heat exchanger space into the reservior tank above during the recharging period.

Typically, the proportions of the heat exchange chambers could be 2 x 1 x 1/40. More generally, the thickness could be less than 1/10 of the shorter of the length or width of the chambers, and is preferably less than 1/20

Claims

CLAIMS 1. A heat storage unit comprising a heat store, electrical means for heating the heat store, and a heat exchanger in contact with the heat store for heating a fluid to enable heat to be withdrawn from the heat store, the heat exchanger including a chamber defined by opposed plates, the spacing of which is small relative to the lateral dimensions of the plate. 2. A heat storage unit as claimed in claim 1, in which each plate has projections extending towards and in contact with the other plate. 3. A heat storage unit as claimed in claim 2, in which the projections are formed integrally from the plate. 4. A heat storage unit as claimed in any one of claims 1 to 3, in which the plates are welded together around their peripheries. 5. A heat storage unit as claimed in any one of claims 1 to 4, in which the heat exchanger comprises a plurality of such chambers, arranged upright and connected to upper and lower headers. 6. A heat storage unit as substantially as hereinbefore described with reference to the accompanying drawings. AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

1. A heat storage unit comprising a heat store, electrical means for heating the heat store, and a heat exchanger in contact with the heat store for heating a fluid to enable heat to be withdrawn from the heat store, the heat exchanger including a chamber defined by opposed plates, the spacing of which is small relative to the lateral dimensions of the plate, and the heat store including a stack of bricks in contact with a face of the chamber.

2. A heat storage unit as claimed in claim 1, in which the heat store includes another stack of bricks in contact with the other face of the chamber.

3. A heat storage unit as claimed in claim 1 or claim 2, in which each plate has projections extending towards and in contact with the other plate.

4. A heat storage unit as claimed in claim 3, in which the projections are formed integrally from the plate.

5. A heat storage unit as claimed in any one of claims 1 to 4, in which the plates are welded together around their peripheries.

6. A heat storage unit as claimed in any one of claims 1 to 5, in which the heat exchanger comprises a plurality of such chambers, arranged upright and connected to upper and lower headers.

7. A heat storage unit as substantially as hereinbefore described with reference to the accompanying drawings.